Microelectrodes are major tools in neurophysiological research. By means of very fine electrodes inserted into brain matter the electrical activity generated by neural tissue can be monitored. The microelectrodes most widely used in the field are single strands of insulated metal wire, sharpened and exposed at the tip, or glass micropipettes. These electrodes are only able to sense the electrical activity of single neurons or average activity of a group of neurons at one point. For at least two reasons it is often advantageous to sense multiple neighboring neurons: the work required for each single analysis of neurons within a class is decreased; and data can be gathered on neuronal interactions. Although simultaneous recording from neighboring neurons by separate microelectrodes has been attempted, it is a very difficult procedure.
Multielectrode probes have been suggested by Wise et al. in "An Integrated Circuit Approach To Extracellular Microelectrodes," IEEE Transactions On Biomedical Engineering, Vol. BME-17, No. 3, July, 1970, pages 238 to 247, and by Pochay et al. in "A Multichannel Depth Probe Fabricated Using Electron Beam Lithography," IEEE Transactions On Biomedical Engineering, Vol. BME-26, No. 4, April 1979, pages 199 through 206. At page 241 of the Wise et al. publication, a probe having three electrodes protruding from its tip is shown. The electrodes are supported by a glass substrate and are coated by electrical insulation. In the more recent Pochay et al. article, three recording sites are formed around the circumference of a glass pipette and are exposed through an upper layer of insulation. The device of the Pochay et al. article has a very small volume along its tip and thus minimizes damage to the brain tissue. However, that device requires the use of a very sophisticated three dimensional fabrication technique and, due to its very thin tip, is subject to breakage during handling.
The quality of data about neuronal group interactions obtained from microelectrodes is directly related to the number of simultaneous recordings made. It would be desirable, for example, to sense the electrical activity of neurons at twenty or more sites through the cortex, the outer layer of the brain. The simultaneous response of neighboring neurons to stimuli would provide a greater insight into the group interaction of neurons.
An object of this invention is to provide a multielectrode probe suitable for sensing the electrical activity of neural tissue at a plurality of sites, the volume of the electrode being small enough to minimize damage to the brain tissue even where as many as 20 sensing sites are provided. A particular object of this invention is to provide such a probe which can be easily handled without breakage and which can be fabricated inexpensively. The increased number of sites increases testing efficiency by increasing the number of cells monitored with each positioning of the microelectrode. Also, parallel recording of neurol groups is possible with a single microelectrode.